The public switched telephone network (PSTN) in the United States has become the most reliable network in the world. Unlike packetized networks such as the Internet and enterprise networks where outages occur often and are expected, customers have come to expect their telephone service to be reliable and high quality. The technology of the PSTN has been developed over decades to achieve the quality and reliability that people have come to expect of it. At the heart of the reliability of the PSTN is redundancy. Redundancy in carrier class networks is the ability of telecommunications equipment to continue operation without service outages or degradation in case of failure of any component of the telecommunications network.
With the growth of data networking, particularly the Internet, there has been a push to converge the voice network (PSTN) with the data network inside carriers. Such a convergence would save carriers enormous amounts of money by only having to maintain one network instead of two parallel networks. The problem with such a convergence has been the lack of quality of service and reliability in the Internet, particularly for real-time applications such as voice over IP (VoIP), the Internet equivalent of the PSTN phone service.
The power of internet protocol (IP) networks, such as the Internet, is their connectionless method of transporting data from source to destination. The nature of this connectionless transport is embodied in the “forward and forget” paradigm of the IP network's most powerful tool: the router. The Internet was designed to be able to route around individual pieces of equipment that may be down, which means that end to end the Internet is relatively reliable. This strength however can cause problems for real-time traffic. Since any individual packet making up a flow, or session, such as a voice call, can be routed differently from the other packets making up the call delay is often introduced, thereby degrading the quality of the voice call. Further, since internet protocol (IP) networks such as the Internet are built on a “forward and forget” paradigm, an IP network is unable to distinguish a packet of a voice call from a packet containing an email message even though the expectations in quality of service differ greatly between the two. Without information about packets or flows that the network could use to treat one packet or flow differently than the rest, the network must treat every packet and flow the same, resulting in the best efforts form of quality of service, as anyone who has ever used the Internet is familiar with.
To avoid the “forward and forget” paradigm, the network needs to be able to learn and maintain knowledge of the characteristics of the data packets and flows passing through it. Additionally, the network should learn and remember the events that are contained within the contents of those data packets or flows. With this knowledge, the network would have the information necessary to distinguish between packets and flows, and give those with particular characteristics or events treatment different from the other packets in the network. For example, if the network was able to recognize a streaming video flow, the network could assign a higher quality of service to that flow to ensure that it passed through the network in the most efficient fashion.
Any piece of equipment providing intelligence to the network will be useless unless always up and running. Outages in an intelligent network processing system would negate the advantages it provides in adding intelligence to the network. To achieve the quality and reliability expected from phone service, any network processing system handling VoIP traffic must have the redundancy capabilities to ensure always on service.
Accordingly, what is needed is a network processing system that has a redundant architecture capable of maintaining service despite an outage in any particular system or component.